Geostuff offers a selection of wall-lock borehole geophones.
Model BHG-2 (pictured on the right in photograph) contains a 3-component geophone in an X-Y-Z orientation. The outside diameter is 1.85 inches (47 mm), small enough to fit inside a schedule-40, 2-inch plastic pipe.
The clamping mechanism is a robust, steel spring compressed by a DC electric motor. There are no rubber bladders to break or tubes to leak, and operation is relatively independent of depth. BHG-2 models have been used to depths of 500 meters (consult factory for details). The standard geophone elements are high-output, 15 Hz natural frequency that can operate with the tool vertical or horizontal. Elements are also available with 10, 14, 28 or 40 Hz natural frequencies.
The BHG-3 (pictured, center) includes three geophone elelments, plus a fluxgate compass and a servo mechanism which automatically rotates the horizontal geophones to the azimuth of your choice.
The BHGC-1 Controller is available. This unit switches power to the clamp mechanism and compass, and also directs the geophones signal to your standard seismograph.
The clamping mechanism is operated by a DC motor, actuated by power sent down two of the conductors. The polarity is reversed to release the clamp.
The surface controller provides power to the clamp mechanism and connects the geophone signals to your standard seismic instrument.
The BHGC-1b controller operates one geophone, while the BHG-4 controller can operate up to four separate geophones. The controller requires 24 volts DC power with cables up to 200 meters length, or more voltage for longer cables.
An optional, internal rechargable battery with AC charger is available and recommended.
The cable is a 7-conductor copperweld with Kevlar® braid and polyurethane jacket, specially manufactured for Geostuff. An SU-8F waterproof connector is molded on the wet end and a Cannon NK-27-21C on the dry end. The cable can be easily disconnected from the geophone for ease of handling. Extension cables are also available with a pair of male and female connectors so that the cable can be temporarily lengthened for unusually deep holes. Popular lengths are normally available from stock, and custom lengths are available on special order.
The standard clamp mechanism works for holes between 2 and 6 inches (48-150 mm), but for large holes the Big Hole Kit is available. This mechanism easily installs in place of the standard spring on any of the BHG series and will expand up to 19 inches (48 cm).
Geostuff has published a tutorial paper describing the field methods for conducting borehole shear wave surveys. To download a copy, click Downhole Shearwaves